Three years ago, the court signaled that part of the law may no longer be needed, and the law’s challengers said the re-election of the nation’s first black president is proof that the nation has moved beyond the racial divisions that gave rise to efforts to protect the integrity of elections in the South.

The law “is stuck in a Jim Crow-era time warp,” said Edward P. Blum, director of the Project on Fair Representation, a small legal foundation that helped organize the suit.

Civil rights leaders, on the other hand, pointed to the role the law played in the recent election, with courts relying on it to block voter identification requirements and cutbacks on early voting.

“In the midst of the recent assault on voter access, the Voting Rights Act is playing a pivotal role beating back discriminatory voting measures,” said Debo P. Adegbile, the acting president of the NAACP Legal Defense and Educational Fund.

The Supreme Court’s ruling on the law, expected by June, could reshape how elections are conducted.

The case concerns Section 5 of the law, which requires many state and local governments, mostly in the South, to obtain permission, or “preclearance,” from the Justice Department or a federal court before making changes that affect voting. Critics of the law call the preclearance requirement a unique federal intrusion on state sovereignty and a badge of shame for the affected jurisdictions that is no longer justified.

The preclearance requirement, originally set to expire in five years, was upheld by the Supreme Court in 1966 as a rational response to the often flagrantly lawless conduct of some Southern officials then.

Congress has repeatedly extended the requirement: for 5 years in 1970, 7 years in 1975, and 25 years in 1982. Congress renewed the act in 2006 after holding extensive hearings on the persistence of racial discrimination at the polls, again extending the preclearance requirement for 25 years.

But it made no changes to the list of jurisdictions covered by Section 5, relying instead on a formula based on historical practices and voting data from elections held decades ago. It applies to nine states — Alabama, Alaska, Arizona, Georgia, Louisiana, Mississippi, South Carolina, Texas and Virginia — and to scores of counties and municipalities in other states.

Should the court rule that Congress was not entitled to rely on outdated data to decide which jurisdictions should be covered, lawmakers could in theory go back to the drawing board and re-enact the law using fresher information. In practice, given the political realities, a decision striking down the coverage formula would probably amount to the end of Section 5.

In May, a divided three-judge panel of the United States Court of Appeals for the District of Columbia rejected a challenge to the law filed by Shelby County, Ala. Judge David S. Tatel, writing for the majority, acknowledged that “the extraordinary federalism costs imposed by Section 5 raise substantial constitutional concerns,” and he added that the record compiled by Congress to justify the law’s renewal was “by no means unambiguous.”

“But Congress drew reasonable conclusions from the extensive evidence it gathered,” he went on. The constitutional amendments ratified after the Civil War, he said, “entrust Congress with ensuring that the right to vote — surely among the most important guarantees of political liberty in the Constitution — is not abridged on account of race. In this context, we owe much deference to the considered judgment of the people’s elected representatives.”

The dissenting member of the panel, Judge Stephen F. Williams, surveyed recent evidence concerning registration and turnout, the election of black officials, the use of federal election observers and suits under another part of the law.

Some of that evidence, he said, “suggests that the coverage formula completely lacks any rational connection to current levels of voter discrimination,” while other evidence indicates that the formula, “though not completely perverse, is a remarkably bad fit with Congress’s concerns.”

“Given the drastic remedy imposed on covered jurisdictions by Section 5,” he wrote, “I do not believe that such equivocal evidence can sustain the scheme.”

The Supreme Court has already once considered the constitutionality of the 2006 extension of the law in a 2009 decision, Northwest Austin Municipal Utility District Number One v. Holder. But it avoided answering the central question, and it seemed to give Congress an opportunity to make adjustments. Congress did not respond.

At the argument of the 2009 case, Justice Anthony M. Kennedy questioned whether the distinctions drawn in the 2006 law reflect contemporary realities.

“Congress has made a finding that the sovereignty of Georgia is less than the sovereign dignity of Ohio,” Justice Kennedy said. “The sovereignty of Alabama is less than the sovereign dignity of Michigan. And the governments in one are to be trusted less than the governments in the other.”

“No one questions the validity, the urgency, the essentiality of the Voting Rights Act,” he added. “The question is whether or not it should be continued with this differentiation between the states. And that is for Congress to show.”

In the end, the court, in an 8-to-1 decision, ducked the central question and ruled instead on a narrow statutory ground, saying the utility district in Austin, Tex., that had challenged the constitutionality of the law might be eligible to “bail out” from being covered by it. Still, Chief Justice John G. Roberts Jr., writing for the majority, was skeptical about the continued need for Section 5.

“The statute’s coverage formula is based on data that is now more than 35 years old,” he added,“and there is considerable evidence that it fails to account for current political conditions.”

Having said all of that, and acknowledging that the court’s alternative ruling had stretched the text of the statute, Chief Justice Roberts said the court should avoid deciding hard constitutional questions when it could. “Whether conditions continue to justify such legislation is a difficult constitutional question we do not answer today,” he wrote.

On Friday, in agreeing to hear the case, Shelby County v. Holder, No. 12-96, the court indicated that it is prepared to provide an answer to the question it left open three years ago.

A version of this article appears in print on November 10, 2012, on page A1 of the New York edition with the headline: Justices to Revisit Voting Act In View of a Changing South. Order Reprints|Today's Paper|Subscribe